1. Field of the Invention
This invention relates generally to a compressed gas storage tank having a heated gas outlet channel and, more particularly, to a compressed gas storage tank that employs a low cost generator for generating electricity as a result of gas flow from the tank that is used to heat an electrical heater to heat the tank material proximate the tank sealings and the gas.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cell systems as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines.
Typically hydrogen is stored in a compressed gas tank under high pressure on the vehicle to provide the hydrogen necessary for the fuel cell system. The pressure in the compressed tank can be upwards of 700 bar. In one known design, the compressed tank includes an inner plastic liner that provides a gas tight seal for the hydrogen, and an outer carbon fiber composite layer that provides the structural integrity of the tank. At least one pressure regulator is typically provided that reduces the pressure of the hydrogen within the tank to a pressure suitable for the fuel cell system.
It is important that the compressed hydrogen stored in the tank be prevented from leaking or diffusing out of the tank. Because hydrogen is a very light and diffusive gas, sealing the tank is typically difficult, especially around the connection area to the outside of the tank. Thus, it is desirable to reduce the number of sealings and the complexity of the connection area to the tank. Also, typically the connecting structures in the tank are made of different materials, which also make the sealing more difficult.
As the hydrogen is removed from the compressed tank, the pressure of the hydrogen decreases. When the pressure of a gas is reduced and the volume does not change, the temperature of the gas will also decrease. If the flow rate of the hydrogen flowing out of the tank is high enough and/or the temperature of the environment is low enough, the temperature in the tank can fall below −80° C. Typically it is possible to limit the hydrogen flow rate so that −80° C. is the lowest temperature that occurs within the tank. If the temperature of the hydrogen within the tank decreases beyond a certain temperature, such as −80° C. around the liner and −40° C. at the tank seals, including O-rings and other sealings, the materials become brittle and possibly damaged, affecting the tank's gas tight performance. Therefore, there are generally limits as to how fast hydrogen and/or for how long hydrogen can be removed from the compressed tank in a fuel cell system. However, this could be undesirable because the output current of the fuel cell stack could be limited accordingly.
It is known to heat the connector area of the tank with an electrical heating element or hot water so that the temperature of the O-rings and other components are maintained above a desirable temperature. However, the known heating solutions are typically complex and costly because the entire connector area is heated, which requires a substantial amount of energy.
Also, it has been proposed in the art to increase the integrity of the various sealings that seal the opening of the compressed gas storage tank. However, as the hydrogen is removed from the tank over a number of cycles, the sealing integrity of the seals may be reduced. Further, providing reinforced seals and the like adds a significant cost to the tank.